Hollow core doors are used in both interior and exterior applications. Many hollow core doors are made from door skins formed from wood composite materials. These wood composite materials may include particle board, flake board, hard board, and medium density fiberboard (“MDF”). The wood composites often utilize a resin binder, which frequently is a thermal setting resin, in order to maintain the wood fibers forming the composite in solid form.
A hollow core door may be of the “flush” type, that is one that is flat or planar on both major surfaces (i.e. both door skins are flat and do not include panels molded therein). Alternatively, a hollow core door may be of the “molded” type, that is one having a series of three-dimensional panels or the like formed or molded into the skins as they are being manufactured.
Standard molded door skins are formed from a relatively thick non-solid mat or bat of material, which is thereafter compressed in a press to a relatively thin, final thickness. The mat can be produced from either dry or wet fibers. If the mat has a very high water content, with the result that water is squeezed out during the pressing operation. The press may be a multiple platen press, having a series of skin forming pockets. Because the mat is in a flexible state prior to the pressing operation, then the resulting solid skin has sharply defined features acceptable to consumers because the wood fibers can flow in order to conform to the mold. Due in part to the high capital costs involved to build plants to make molded skins, manufacturers frequently require that individual orders be for a large number of skins in order to permit maximum operating efficiencies. Smaller orders become cost prohibitive.
Flush door skins on the other hand may be made in a similar manner as molded skins, except that the original mat or bat of wood fibers is pressed flat, and is not three-dimensionally molded to form panels or the like. Alternatively, a continuous belt press may be used for flat skins. Thus, a flush door skin originates from a relatively thick non-solid mat or bat of wood-like fibers, which is pressed into a planar or flat shape to define the flush solid skin. This means that standard medium density fiberboard, or hardboard may be used.
Standard molded door skins are relatively expensive, because the capital cost is quite high due to the need for dies, presses, and the like. The flat or planar skins used for flush doors, on the other hand, are relatively inexpensive, but do not provide the aesthetic features often desired by consumers.
Because of the cost differential between a wood composite “flush” or “flat” skin and a wood composite “molded” skin, attempts have been made to transform flush skins into molded skins in an effort to more inexpensively produce molded door products. Such prior efforts have not resulted in commercially acceptable door skins, principally because the appearance of the surface has typically not been satisfactory. Prior efforts to transform flush skins into molded skins have generally resulted in the final molded skin having a cracked, marred, or otherwise aesthetically displeasing configuration and/or appearance.
It is apparent from the above that there exists a need in the art for a method of manufacturing a molded door skin from a flat wood composite blank which permits a standard flush or flat skin blank to be used as the base material, and which results in a molded door skin having features and surface characteristics acceptable to consumers. Yet a further need in the art is a molded door manufactured from flat wood composite door skins, which has suitable resistance to moisture, so that the door may be used for exterior applications.
It is a purpose of this invention to fulfill the above-described needs in the art. In commonly owned U.K. Application No. 9707318.3), there is disclosed a method of making a hollow core door by reforming flush or flat door skins into molded skins via a press, wherein pressure applied to platens of the press is increased in a series of steps. It has been found that the method of the prior application can be improved upon, as set forth below, to enable more efficient flat skin shaping, and improved strength to the end product door.